Alliances aren't at all about trust, they're about what can you do for me and what can I do for you. Currently Africa's interests is met with the Chinese, there's no guarantee that it'll be so in the future. In fact, there may come a time when African countries may instead become the US's allies – the world is funny that way – and generally that's how state alliances work: today's enemy may be tomorrow's friend and vice-versa. There's little space for morals, or even ethics, the goal is progress.